1. Field of the Invention
The present invention relates to an engine control method for controlling the operation of an engine using fuel mixture.
2. Description of the Related Art
Recently attention has been paid to methanol as low-pollution fuel, and a methanol engine has been developed accordingly. It is however almost impossible to replace gasoline with methanol as fuel for every car. It is expected that both the methanol fuel and the gasoline are used at least temporarily at the time of such replacement takes place.
To cope with such a situation, it is proposed to introduce a Flexible Fuel Vehicle (hereafter referred to as "FFV") which can use either the gasoline fuel or the methanol. That is, the FFV has more freedom in using fuel.
To take an accurate timing of igniting an engine and precisely control the amount of fuel injection, the FFV detects a blend ratio or mixing ratio of the gasoline to methanol, and will control individual sections of the engine. Blend ratio detecting means in this case is a blend ratio sensor which is installed directly in the fuel supply system and directly detects a blend ratio. This sensor has been studied and improved, and nowadays is used.
The octane number of the fuel mixture varies depending on the blend ratio. This particularly requires adjustment of the ignition timing according to the blend ratio, and its compensation process is performed.
If the blend ratio sensor is damaged or fails, or if both the blend ratio sensor and a knock sensor fail when the blend ratio is estimated on the basis of the output of the knock sensor, the control blend ratio would greatly deviate from the real ratio.
The engine control under the improper ignition timing will cause the engine to improperly function. The control range of the ignition timing of the FFV engine is set large compared to that of the ordinary gasoline engine. Therefore, igniting the engine at the incorrect time may damage the engine, which raises a problem.
The present invention aims to provide a method for acquiring the proper control blend ratio and ignition timing even when the blend ratio sensor and knock sensor fail, thereby performing satisfactory operation control of the engine.